Control system for fuel control under starting and excessive speed conditions in an internal combustion engine

ABSTRACT

A pulse sequence having a frequency proportional to engine speed is converted to a D.C. voltage decreasing in amplitude with pulse frequency. When this voltage has predetermined magnitude, starting fuel control switch circuit energizes a relay causing maximum fuel injection. First and second rectifier means having different frequency varying characteristics furnish, respectively, a positive and negative voltage. When combination of positive and negative voltage reaches a determined magnitude, excess speed control switching circuit energizes a relay furnishing a control signal for minimum injected fuel.

U mted States Patent 1151 3,693,603

Lemanczyk I [4 1 Sept. 26, 1972 CONTROL SYSTEM FOR FUEL 3,089,475 5/1963 Kohler 123/139 ST CONTROL UNDER STARTING AND 3,332,406 7/1967 Perry ..123/102 EXCESSIVE SPEED CONDITIONS IN 3,407,793 10/1968 Lang 123/32 EA AN INTERNAL COMBUSTION ENGINE 3,425,401 2/ 1969 Lang ..123/32 EA 3,525,017 8/1970 Rosenberg ..123/32 EA [721 222" Lemanczyk Stuttgart 3,548,792 12/1970 Palmer ..123/32 EA y 3,573,482 4/1971 Brooks ..123/179 G [73] Assignee: Robert Bosch Gmbl-I, Stuttgart, Ger- 1 ma y Primary Examiner-Laurence M. Goodridge Assistant Examiner-Ronald B. Cox 22 Fl d: Dec. 14 1970 I l Attorney-Michael s. Striker [21] Appl. No.: 97,980

[57] ABSTRACT Foreign ApPlicafion Priority Data A pulse sequence having a frequency proportional to 13, 1969 Germany p 19 62 573 1 engine speed is converted to a D.C. voltage decreasing Aug. 29, 1970 Germany ..P 20 42 914.5 in amplitude with Pulse frequencywhen this voltage has predetermined magnitude, starting fuel control 52 us. Cl ..123/102 R, 123/179 0, 123/179 1., switch circuit energizes a relay causing maximum fuel 123/32 EA, 123/139 E injection [51] Ila. CI- ..F02d 11/10 F9211 17/00 First and second rectifier means having different [58] new of searchmlnnz 179 179 frequency varying characteristics furnish, respectively, 123/32 139 139 ST a positive and negative voltage. When combination of positive and negative voltage reaches a determined [56] References and magnitude, excess speed control switching circuit UNITED STATES PATENTS energizes a .relay furnishing a control signal for minimum injected fuel. 2,499,706 3/1950 Ward ..123/32 AE 2,984,232 5/1961 Arndt ..123/139 ST 16 Claims, 2 Drawing Figures PAIENTEDserzs m2 SHEET 1 OF 2 FIG] INVENTOR Rudolf LEMANCZYK his ATTORNEY CONTROL SYSTEM FOR FUEL CONTROL UNDER STARTING AND EXCESSIVE SPEED CONDITIONS IN AN INTERNAL COMBUSTION ENGINE BACKGROUND OF THE INVENTION This invention relates to circuits used in the control of electronically controlled internal combustion engines and more specifically, Diesel engines. In particular, this invention relates to such engines which have a of the injection element is determined by an electrical control signal.

It is well known that the operating characteristics for Diesel engine can be improved by regulating its operation electronically. Further, a single type of regulator may be matched to a plurality of engine types with the aid of electrical adjustment means. Furthermore, it can be reliably prevented that the exhaust gas of the engine contains unburned fuel, thereby decreasing pollution. For example, the fuel may be fed into the engine by means of an injection pump whose injection element is electrically controlled. Thus, the injection pump need not comprise mechanical flywheel regulators or similar arrangements. Furthermore in general, this type of Diesel engine needs a positive means for preventing its speed from exceeding a predetermined maximum speed. This is due to the fact that in electronically controlled system it is possible that failure of a component could result in such excessive speeds and if no further means for preventing such excessive speeds are provided, mechanical damage can result. Such component failure can of course never be completely eliminated, especially since the regulating systems are relatively complicated. A regulating system may for example comprise circuitry to simulate the desired motor characteristics. Under normal conditions, this simulator will, in itself, result in a limiting of the speed to a e j SUMMARY OF THE INVENTION It is an object of the present invention to furnish an additional speed control as described above to prevent excessive speeds in case of. the failure of the normal regulating system.

It is a further object of the invention to furnish automatically an oversupply of fuel during the starting phase of the engine so that the motor upon starting is driven to a speed higher than the desired no-load speed, at which point the excessive fuel supply is shut off and the standard control system takes over.

It is a further object of the present invention to furnish such a system wherein the failure of a component, and in particular of a component in the excesfurnished are first and second rectifier means each hav-.

ing an input connected to the speed sensor means and furnishing, at a first rectifier output terminal, a first rectifier output signal having a first polarity at engine speeds exceeding a predetermined engine speed. The first and second rectifier means further have a second rectifier output terminal whereat is furnished a second rectifier output signal having a second polarity opposite to said first polarity. Finally, a starting fuel control switching circuit has an input connected to said second rectifier output terminal and said speed signal furnishing means. Said starting fuel control switching circuit furnishes said first fuel control signal in response to a predetermined combination of said second rectifier output signal and said speed signal. The excess speed control is provided by an excess speed control switching circuit having an input connected to said first rectifier output terminal and furnishing said second fuel control signal in response to said first rectifier output signal.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows an embodiment of the present invention effecting speed limiting at a predetermined maximum speed which remains the same under all engine operating conditions; and

FIG. 2 shows an embodiment wherein said predetermined maximum speed varies in dependence upon engine operating conditions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will now be discussed with reference to the drawing.

The Diesel engine shown at reference numeral 10 of FIG. 1 is provided with fuel by an injection pump 11, whose injection element determining the quantity of fuel to be injected per operating cycle is shown as block 12. The fuel control signal which determines the position of this element is the voltage appearing between lines and 61 in the Figure. Further, a feedback signal for a control loop to be briefly described below is furnished by block 13 and is a signal proportional to the position of the injection element and therefore the quantity of fuel being injected. Furthermore, pump 11 drives a speed sensor 14, at whose output is generated an alternating voltage whose frequency is proportional to, the speed of the pump and therefore the speed of the engine. The so-generated alternating voltage is applied to the input of an overdriven amplifier at hose output appears a pulse sequence whose repetition frequency is proportional to the speed of the injection pump. The output of the overdriven amplifier 15 where this pulse sequence appears is applied to speed signal furnishing means, namely a switching stage 16 followed by a filter 17. In switching stage 16, the pulse sequence is differentiated causing negative trigger pulses to be furnished which are applied to a monostable multivibrator which remains. in its unstable state for a predetermined constant time constant. Thus, an interrupted D.C. voltage appears at the output of switching stage 16 whose average is proportional to engine speed. This interrupted,D.C. voltage is applied to a filter 17 at whose output appears a DC. voltage having a strictly limited A.C. component. Further, temperature compensation is applied to the filter to improve its accuracy so that temperature-caused changes in components such as transistors, do not affect said accuracy. The socalled speed signal or speed voltage appearing at the output of filter 17 is applied to a standard regulating circuit which is not the subject of the present invention, but which comprises circuit simulating motor characteristics, labelled 19 in FIG. 1. The output of this simulator circuit is applied to the input of a control amplifier 20 and serves as a reference input. A second input of amplifier 20 is the feed-back signal derived from box 13. The output of amplifier 20 is thus a function of the difference between the reference signal as supplied by stage 18 and the feedback signal supplied by stage 13. This difference, after power amplification by power amplifier 21, is the signal on line 61. It is seen that under normal operating conditions, the fuel supplied to the engine will be determined by the signal furnished by power amplifier 21 relative to the positive supply potential furnished on line 60 via contacts u2 of relay U which will be discussed below. *)(The operation mode of an electrically controlled mechanical injection pump is schematically described in the US. vPat. No. 3 407 973.)

It should further be mentioned that for reasons of safety, the output of filter 17 is a voltage which decreases with engine speed. Thus if this voltage falls due to component failure, the result is that a minimum, or zero, amount of fuel is injected and not a maximum amount. It should further be noted that the simulating circuit 19 may have other inputs as for example the gas pedal shown as l9 with an underlining in FIG. 1. The control system is only shown here to indicate how the features of the present invention are interconnected therewith. In itself, it is not a subject of the present invention.

The starting fuel control switching means are shown in FIG. 1 as box 25, while the excess speed control switching means are labelled 26. Both of these switching circuits are Schmitt triggers. Schmitt trigger 25 comprises transistors T27, T28 and T29. The emitters of all the transistors T27 to T29 are connected to line 30 which is connected to ground. Collectors of transistors T27 and T28 are connected to a line 32 via resistors R31 and R32, respectively. Line 33 is connected to a stabilized positive voltage supply labelled +U The collector of transistor T28 is further connected to line 30 via a series connection of two resistors R34 and R35. The base of transistor 29 is connected to the common point of resistors R34 and R35. A starting relay S has a coil connected between the collector of transistor T29 and a positive voltage supply U,,. A diode 36 is connected in parallel with relay coil S in order that transient voltage spikes are prevented during the disconnection of the coil. Such spikes would otherwise result from current interruption through such an inductance. The cathode of diode D36 is connected to terminal +U,,. The collector of transistor T28 is connected to the base of transistor T27 by a resistor R37. This resistance R37 can be used to lend a hysteresis type of behavior to this Schmitt trigger. That is, the starting and cut-out points of this switch can thus be different. Schmitt trigger 26 is identical to Schmitt trigger circuit 25 except for a resistance 38 which connects the base of transistor T27 with the stabilized voltage source +U,, Further discussion of the Schmitt trigger 26 is therefore not essential. An excess speed relay U is connected between the collector of transistor T29 and the voltage source +U in a manner analogous to the connection of relay S in Schmitt trigger 25. In the same way, and for the same reason, a diode 36 is connected in parallel with this coil.

The signal determining the condition of switch 26 is applied to the base of transistor T27 and is derived from first and second rectifier means, namely circuits 49 and 42. The latter comprises three diodes D43, D44, and D45 connected in series. A capacitor C46 is connected in parallel with these diodes. The output of amplifier 15, an A.C. voltage, is applied to the common point of diodes D43 and D44 via a coupling capacitor C47. The anode of diode D43 is connected to the base of transistor T27 via an adjustable resistance R41. A second adjustable resistor R48 connects the base of transistor T27 with the anode of diode D43. The first rectifier means 49 are constructed similarly to rectifier means 42. They comprise a series circuit of diodes D50 and D51. The anode of diode 50 is connected to a line 30 which is connected to line 30 and thus to ground potential. The cathode of diode 51 is connected to the base of transistor T27 via an adjustable resistor R52.

The common point of adjustable resistors R52 and R41, which pointis also at the same potential as the base of transistor T27, is herein referred to as the first rectifier output terminal. The second rectifier output terminal is the common point of diode D43 and the other terminal of resistance R41. A capacitor C53 is connected in parallel with diodes D50 and D51 and the common point of diodes D50 and D51 are connected to the output of amplifier 15 via a coupling capacitor C54. The base of transistor T27 is further connected with the output of filter 17 by means of an adjustableresistance 55. As mentioned above, the signal controlling the movement of the injection element is furnished between lines 60 and 61. If both relays S and U are deactivated, the fuel supply is controlled by the normal control system. This is the condition shown in the Figure. Thus it is seen that line 60 is connected to second relay, while relay S is herein referred to as the first relay. Thus the second relay contacts comprise the pair of normally closed contacts mentioned above and further a normally open contact connected via a control lamp to ground potential. The movable arm associated with the second relay contacts is connected to +U,, and it is thus obvious that activation of relay U causes energization of the control lamp and de-energization of line 60. Relay U has further a pair of normally open contacts, one side of which is connected to the collector of transistor T29 and thus to one end of the coil of relay U. The other terminal of this normally open contact is connected to ground potential via a pair of normally closed contacts of relay S. Specifically, a movable arm of relay S is connected to ground poten tial, is normally connected to the above-mentioned pair of normally open contact of relay U and, upon activation of relay S, is connected to line 61 via a second one of the first relay contacts. Thus activation of relay S causes line 61 to be connected to ground potential. Further, connected between line 60 and ground, is the coil of a further, independent excess speed shut-off device labelled 63. This may, for example, be a solenoid and operates a valve preventing the build up of pressure in the injection pump and thereby preventing fuel injection. This system is used in case of failure of the main system. 7

The above-described arrangement operates as follows:

First, let it be assumed that the engine 10 and all of the electronic circuits are disconnected. If now the electronic circuits are energized, both the Schmitt trigger 25 and Schmitt trigger 26 are temporarily put into their operating positions, that is the states in which relays S and U are energized. Transistor 27 of switch 25 receives a positive bias from the output of filter 17, causing it to become conductive. This causes transistor T28 to block in turn causing the base of transistor T29 to receive a positive voltage causing it to become conductive and thereby energizing the relay S. Similarly, the excess speed switch 26 is first switched on, because transistor 27 gets a positive voltage via resistor R38.

The conductivity of transistor T27 causes transistor T28 to block and thereby causes transistor T29 to become conductive causing relay U to be energized. Under these conditions, movable arm s connects line 61 to ground, while the movable arm a connects the control or indicator lamp 62 to the positive voltage source +U,,. Thus the indicator lamp lights upon initiation of the starting procedure and before the engine starts to turn. If the control lamp 62 lights during operation of the engine, it indicates that the engine is exceeding its maximum permissible speed. However, its lighting, while the engine is standing still, indicates the correct functioning of the excess speed switching means 26 so thatthe operation of this switch is tested every time the engine is started. The components of rectifier 42 are so chosen that a low voltage appears at its output even for very low frequency input voltages. The frequency characteristics of this rectifier are determined by the joint characteristics of coupling capacitor C 47 and resistance R 41. The negative voltage appearing at the second rectifier outputterminal is applied to the base of transistor T27 via resistance R41 and causes this transistor to block. This in turn causes transistor T28 to become conductive and transistor T29 to block, causing relay U to be de-energized. Therefore variable arm :4 returns to its normally closed position with line 60, connecting this line to voltage +U Control lamp 60 extinguishes and, since relay S is still energized, the voltage appearing across line 60 to line 61 is the full-line voltage causing maximum fuel injection. As mentioned above, filter 17 has an output voltage which decreases for increasing frequency of its input voltage. The operating characteristics of rectifier 42 are obvious from the circuit diagram. Diode 44 is used only to compensate for temperature changes in diodes 43 and 45. Capacitor C46 serves to smooth the DC. voltage. It will be noted that the output of this rectifier is a negative DC. voltage, which is the only negative voltage used throughout the equipment.

If the starting process is now interrupted although the engine 10 has not yet started, the voltage at the second rectifier output terminal will decrease slowly towards zero. Without further equipment, it is possible to use this voltage to energize a circuit for blocking any possible re-start. If the voltage has decreased greatly, transistor 27' becomes conductive so that relay U becomes activated, disconnecting line 60 from U,, that is causing minimum fuel injection.

However, if the engine starts, its speed will first increase since the maximum fuel is being injected. An increase in engine speed causes a decrease in speed voltage, namely the output voltage of filter 17, which is connected to the base of transistor T27 via resistance R55 R55 is so adjusted that transistor 27 blocks when the voltage is less than a predetermined voltage. As soon as transistor T27 blocks, relay S is de-activated. This causes movable arm s to return to its de-activated position disconnecting line 61 from ground and connecting it with the output of power amplifier 21. ln this case now the injection element is controlled by a fuel control signal which is the voltage difierence between the supply +U, and the output of amplifier 21. The injection element will thus assume the position which corresponds to the value supplied by the simulating stage 19. As discussed above, the output of stage 19 serves as an input to the feedback system whose feedback signal is supplied by stage 13, thereby allowing close regulation of the position of the injection element to the value determined by stage 19.

If now a malfunction occurs so that the speed of the engine exceeds the maximum permissible speed, the output signal of the first rectifier means 49 becomes effective at the first rectifier output terminal causing transistor T27 to receive a positive voltage at its base. This causes this transistor to be conductive which, as explained above, causes transistor T29 to become conductive, energizing relay U. This causes the movable arm a, to connect the indicator lamp to the positive supply terminal. It further closes the normally open contacts u, thereby furnishing a holding circuit which extends from U through the coil of relay U, through the now-closed contact u,, the normally closed contact s of relay S and thence to ground. Relay U therefore remains energized regardless of the state of transistor T29. The fuel injection to the engine is thus limited to the minimum value until the engine is re-started. It is not possible to speed up the engine without such restarting. The holding circuit is only broken when the relay S, the starting control relay, is again energized. Thus, the engine will come to a complete stop whenever relay U is energized.

Since the possibility exists that the electrical portion of the injection element 12 malfunctions, an additional excess speed prevention device 63 is provided as described above. It will be noted that when line 60 is disconnected from +U,,, as a result of activation of relay U, the operating coil of stage 63 is also de-energized. This system is thus so arranged that a valve limiting the fuel supplied to the pump is operated when coil 63 is de-activated.

It will'be noted that in the system shown in FIG. 1, the predetermined maximum speed to which the engine can be operated is the same regardless of load conditions. However, conditions may exist wherein the maximum permissible voltage when the vehicle is driven under load, may be safely exceeded under different operating conditions as, for example, when the engine is coasting downhill. It may thus be desirable to provide a means of changing the maximum permissible speed as a function of the load conditions of the engine. This is accomplished as shown in FIG. 2.

Identical stages and elements in FIG. 2 have the same reference numbers as the corresponding elements in FIG. l. It will be noted that the circuits are completely identical as to the injection system, engine, switch 25, and the first and second rectifier means, as well as the speed signal furnishing means and the control system comprising stages 19, 20 and 21. These, therefore, will not be described again. The only difference between the circuitry shown in FIGS. 1 and 2 are the circuits associated with the excess speed control switching means namely the Schmitt trigger circuit 26. Schmitt trigger 26 of FIG. 2 comprises a transistor T70 and a transistor T71. The base of transistor T70 is connected to the first rectifier output terminal and is further connected to U via a resistor R73. The collector of transistor T70 is connected to terminal +U via a series circuit comprising resistors R 74 and R75. The base of transistor T71 is connected to the common point of resistors R74 and R75, while its collector is directly connected to +U The emitter of transistor T71 is connected to the base of transistor T70 via a resistance. The emitter of transistors T70 is connected to the tap of a voltage divider comprising resistors R77 one of whose terminals is connected to ground, and R78 whose other terminal is connected to a terminal 79. This terminal 79 furnishes the feedback voltage to control amplifier 20, this feedback voltage being a voltage which varies as a function of the position of the injection element. It should be noted that the voltage at terminal 79 decreases with increasing fuel injection, and is therefore a voltage which varies inversely to the applied load. The collector of transistor T71 is connected to cuit 26, which will now be described. It will be noted that in this circuit, as in the circuit of FIG. 1, when T70, the input transistor, becomes conductive, the excessive speed relay U is activated via output transistor, here transistor T82. However, in the circuit of FIG; 2, the switching of transistor T depends not only upon the voltage applied to its base which is the same voltage as in FIG. 1, but also depends upon the voltage at the emitter terminal which depends upon the load of the engine and varies inversely therewith. Specifically, the transistor will become conductive when the voltage furnished at the first rectifier output terminal exceeds the voltage at the emitter terminal by a predetermined threshold value characteristic of the transistor. Under full load conditions, namely under maximum fuel injection conditions, the voltage applied at the emitter via resistor R78 is relatively low, causing transistor T70 to become conductive for substantially the same voltage appearing at the first rectifier output terminal, as was the case in FIG. 1. However, under no load conditions or under low load conditions, the voltage applied at the emitter increases and transistor T70 will not become conductive until the voltage at the first rectifier output terminal exceeds this voltage as stated above. Therefore the maximum permissible speed will increase as the load of the vehicle is decreased. As stated above,

the relay action resulting from the switching of transistor T70 is identical to that resulting from the action of the switching of the corresponding transistor T27 in FIG. 1, and need not be further discussed here. It is to be noted solely that the maximum permissible speed in accordance with the FIG. 2 system is a variable quantity, while that in FIG. 1 is a constant quantity.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a control system for fuel specific under starting and excessive speed conditions in an internal combustion engine, it is not intended to be limited to the details shown, since various modifications and circuit changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended 1. Safety arrangement for an internal combustion engine, comprising, in combination, injection means having an electrically controlled injection element causing maximum fuel injection in response to a first fuel control signal and a predetermined minimum fuel injection in response to a second fuel control signal; speed sensor 7 with increasing engine speed; first and second rectifier means, each having an input connected to said speed sensor means and furnishing, at a first rectifier output terminal, a first rectifier output signal having a first polarity at engine speeds exceeding a predetermined engine speed, said rectifier means further having a second rectifier output terminal furnishing a second rectifier output signal of a second polarity opposite to said first polarity; starting fuel control switching means having an input connected to said second rectifier output terminal and said speed signal furnishing means and furnishing said first fuel control signal in response to a predetermined combination of said second rectifier output signal and said speed signal; and excessive speed control switching means having an input connected to said first rectifier output terminal and furnishing said second fuel control signal in response to said first rectifier output signal.

2. An arrangement as set forth in claim 1, wherein said starting fuel control switching means and said excess speed control switching means each comprise a Schmitt trigger circuit.

3. An arrangement as set forth in claim 2, wherein each of said Schmitt trigger circuits comprises a feedback resistor, thereby permitting two-point operation.

4. An arrangement as set forth in claim 3, wherein said starting fuel control switching means further comprise a first relay having a first relay coil and first relay contacts; and means connecting said first relay coil to the output of said Schmitt trigger circuit in such a manner that current flows through said first relay coil in response to said predetermined combination of signals at said input of said starting fuel control switching means.

5. An arrangement as set forth in claim 4, wherein said excess speed control switching means comprise a second relay having a second relay coil and second relay contacts; and means connecting said second relay coil to the output of said Schmitt trigger circuit in such a manner that current flows through said second relay coil in response to said first rectifier output signal.

6. An arrangement as set forth in claim 5, wherein said first and second fuel control signal respectively comprise a first and second potential difference between a first and second circuit point; means for furnishing a first and second voltage at a first and second voltage terminal respectively; wherein said first relay comprises a variable arm connected to said first voltage terminal and moving from a first to a second of said first relay contacts upon activation of said first relay; means connecting said second of said first relay contacts to said first circuit point; wherein said second relay contacts comprise a pair of normally open contacts connected to said first of said first relay contacts; means connecting said pair of normally open contacts to said second coil; wherein said second relay further comprises a variable arm connected to said second voltage terminal and moving from a first to a second of said second relay contacts upon activation of said second relay; and means connecting said second circuit point to said first of said second relay contact.

7. An arrangement as set forth in claim 6, further comprising an indicator lamp connected between said second of said second relay contact and said first voltagg terminal.

. An arrangement as set forth in claim 1, wherein said first and second rectifier means comprise temperature sensitive components; and wherein said first and second rectifier means further comprise compensating means for compensating for temperature changes in said temperature sensitive components.

9. An arrangement as set forth in claim 8, wherein said temperature sensitive components comprise diodes; and wherein said compensating means comprise an additional diode.

10. An arrangement as set forth in claim 1, wherein said speed signal furnishing means comprise monostable multivibrator means having a stable and an unstable state and switched to said unstable state in response to pulses in said pulse sequence; and filter means having an input connected to the output of said monostable multivibrator means and an output furnishing said speed signal.

11. An arrangement as set forth in claim 1, wherein said injection means comprise an injection pump; further comprising additional fuel cut-off means preventing build up of pressure in said injection pump in response to said second fuel control signal.

12. An arrangement as set forth in claim 1 1, wherein said additional fuel cut-off comprise a solenoid valve.

13. An arrangement as set forth in claim 1, wherein said excessive speed control switching means further comprise biassing means changing the threshold of said excessive speed control switching means as a function of engine load.

14. An arrangement as set forth in claim 13, wherein said excessive speed control switching means comprise a Schmitt trigger circuit, having an input transistor having a base connected to said first rectifier output terminal, and an emitter; wherein said electrically controlled injection element is movable along a predetermined path, the quantity of fuel injected in each operating cycle corresponding to the position of said injection element along said path; further comprising means for furnishing a load voltage corresponding to the position of said element along said path; voltage divider means connected to said means for furnishing a 

1. Safety arrangement for an internal combustion engine, comprising, in combination, injection means having an electrically controlled injection element causing maximum fuel injection in response to a first fuel control signal and a predetermined minimum fuel injection in response to a second fuel control signal; speed sensor means furnishing a pulse sequence having a frequency corresponding to the speed of said engine; speed signal furnishing means connected to said speed sensor means and furnishing a speed signal decreasing in amplitude with increasing engine speed; first and second rectifier means, each having an input connected to said speed sensor means and furnishing, at a first rectifier output terminal, a first rectifier output signal having a first polarity at engine speeds exceeding a predetermined engine speed, said rectifier means further having a second rectifier output terminal furnishing a second rectifier output signal of a second polarity opposite to said first polarity; starting fuel control switching means having an input connected to said second rectifier output terminal and said speed signal furnishing means and furnishing said first fuel control signal in response to a predetermined combination of said second rectifier output signal and said speed signal; and excessive speed control switching means having an input connected to said first rectifier output terminal and furnishing said second fuel control signal in response to said first rectifier output signal.
 2. An arrangement as set forth in claim 1, wherein said starting fuel control switching means and said excess speed control switching means each comprise a Schmitt trigger circuit.
 3. An arrangement as set forth in claim 2, wherein each of said Schmitt trigger circuits comprises a feedback resistor, thereby permitting two-point operation.
 4. An arrangement as set forth in claim 3, wherein said starting fuel control switching means further comprise a first relay having a first relay coil and first relay contacts; and means connecting said first relay coil to the output of said Schmitt trigger circuit in such a manner that current flows through said first relay coil in response to said predetermined combination of signals at said input of said starting fuel control switching means.
 5. An arrangement as set forth in claim 4, wherein said excess speed control switching means comprise a second relay having a second relay coil and second relay contacts; and means connecting said second relay coil to the output of said Schmitt trigger circuit in such a manner that current flows through said second relay coil in response to said first rectifier output signal.
 6. An arrangement as set forth in claim 5, wherein said first and second fuel control signal respectively comprise a first and second potential difference between a first and second circuit point; means for furnishing a first and second voltage at a first and second voltage terminal respectively; wherein said first relay comprises a variable arm connected to said first voltage terminal and moving from a first to a second of said first relay contacts upon activation of said first relay; means connecting said second of saId first relay contacts to said first circuit point; wherein said second relay contacts comprise a pair of normally open contacts connected to said first of said first relay contacts; means connecting said pair of normally open contacts to said second coil; wherein said second relay further comprises a variable arm connected to said second voltage terminal and moving from a first to a second of said second relay contacts upon activation of said second relay; and means connecting said second circuit point to said first of said second relay contact.
 7. An arrangement as set forth in claim 6, further comprising an indicator lamp connected between said second of said second relay contact and said first voltage terminal.
 8. An arrangement as set forth in claim 1, wherein said first and second rectifier means comprise temperature sensitive components; and wherein said first and second rectifier means further comprise compensating means for compensating for temperature changes in said temperature sensitive components.
 9. An arrangement as set forth in claim 8, wherein said temperature sensitive components comprise diodes; and wherein said compensating means comprise an additional diode.
 10. An arrangement as set forth in claim 1, wherein said speed signal furnishing means comprise monostable multivibrator means having a stable and an unstable state and switched to said unstable state in response to pulses in said pulse sequence; and filter means having an input connected to the output of said monostable multivibrator means and an output furnishing said speed signal.
 11. An arrangement as set forth in claim 1, wherein said injection means comprise an injection pump; further comprising additional fuel cut-off means preventing build up of pressure in said injection pump in response to said second fuel control signal.
 12. An arrangement as set forth in claim 11, wherein said additional fuel cut-off comprise a solenoid valve.
 13. An arrangement as set forth in claim 1, wherein said excessive speed control switching means further comprise biassing means changing the threshold of said excessive speed control switching means as a function of engine load.
 14. An arrangement as set forth in claim 13, wherein said excessive speed control switching means comprise a Schmitt trigger circuit, having an input transistor having a base connected to said first rectifier output terminal, and an emitter; wherein said electrically controlled injection element is movable along a predetermined path, the quantity of fuel injected in each operating cycle corresponding to the position of said injection element along said path; further comprising means for furnishing a load voltage corresponding to the position of said element along said path; voltage divider means connected to said means for furnishing a load voltage and having a voltage divider tap; and means connecting the emitter of said input transistor to said tap of said voltage divider.
 15. An arrangement as set forth in claim 14, wherein said load voltage is inversely proportional to the load of said engine.
 16. An arrangement as set forth in claim 1, further comprising circuit means for preventing a restarting of said engine, connected to said second rectifier output terminal. 